Currently, the mobile communication technology has been developed to the 3rd generation. TD-SCDMA (Time Division-Synchronization Code Division Multiple Access) is one of three main 3G standards recognized by ITU (International Telecommunication Union) in May 2000 and by 3GPP (3rd Generation Partnership Project) in March 2001. As a TDM (Time Division Multiplex) 3G standard, TD-SCDMA is a TDM solution with low chip rate (1.28 MCps) in the ITU standards.
Currently, handoff is a necessary process in a cellular mobile communication system, especially for a TD-SCDMA system. As shown in FIG. 1, during the handoff process, a RNC (Radio Network Controller) 1 at the network side transmits a measurement control command to a user equipment (UE) 2 and the UE reports the received measurement result to the RNC according to a certain rule. The RNC determines whether a handoff process should be initiated according to the reported measurement result. If the handoff process is needed, the RNC firstly determines whether there are available resources in a target cell and if there are, the RNC establishes a radio link to the target cell and transmits a handoff control command from the source cell to notify the UE to switch the link to the target cell. However, according to the current baton handoff or hard handoff technology, the UE can only demodulate downlink signals in one cell during the handoff process. Since the UE can only transmit uplink signals to the source cell or the target cell in the uplink direction, the wireless network can only demodulate signals of one uplink.
During the handoff process of the UE from one cell to another, in order to reduce the ping-pong handoff for the current intra-frequency handoff method, the RNC generally sets a strict handoff threshold, for example, only when a pilot signal strength of the target cell is much higher than that of the source cell, the cell handoff process is triggered. If, there are other users existing in the intra-frequency co-time slot of the target cell before the cell handoff process, big interference may be produced at the downlink for users to be subject to the handoff process and if the handoff threshold is not properly set, the communication link between the UE and the source cell may be deteriorated before the handoff process, such that the measurement report transmitted from the UE cannot be properly received by the network or the UE cannot properly receive a handoff command from the network and thus call drop comes into being.
In addition, before the handoff process, if the pilot signal strength of the target cell is stronger than that of the source cell, i.e. in the uplink the signal power of the user to be subject to the handoff process received by the target cell is larger than that received by the source cell, the uplink signal of the user to be subject to the handoff process will produce large interference on the target cell and interference between the intra-frequency co-time slot users in the target cell will increase. Accordingly, the intra-frequency co-time slot users in the target cell will increase the transmitting power under the uplink power control in order to maintain the communication quality, which will increase the interference between the intra-frequency co-time slot users in the target cell. Similarly, the intra-frequency co-time slot users in a neighboring cell will increase the transmitting power under the uplink power control and a positive feedback is formed, which increases an average interference level of the whole network. The call drop in the uplink may happen to the user to be subject to the handoff process because of the increased interference.